Effects of distance on the visual reception of speech.

Abstract

Two talkers with normal hearing and speech presented with voice 240 common nouns (80 monosyllables, 80 trochees, 80 spondees) to six profoundly deaf children whose task was to lipread without acoustic cues at distances from 5-100 ft. Under bright, shadow-free illumination, lipreading performance diminished from 75% correct at 5 ft to 11% correct at 100 ft. Scores varied with distance similarly for both talkers. The stress patterns of the stimulus words influenced their intelligibility, with scores decreasing from spondees to trochees to monosyllables. In a supplementary study, one talker presented two tests of phoneme recognition to the same six deaf children whose task was to lipread from 5, 20, or 70 ft. Identification of consonants in VCV context depended on their place of articulation (front superior to back) and on the surrounding vowel (/a–a/ superior to /i–i/ or /u–u/). Vowel-identification scores were less dependent on distance than were consonant-identification scores. In general, tense (stressed) vowels were more easily identified in /b/-V-/b/ context than were lax (unstressed) vowels.